This invention relates to a method for detecting microorganisms.
It is known from International Publication WO95/33848 that microrganisms such as bacteria can be detected by analysing gases emitted by the microorganisms. International Publication WO 98/29563 describes improvements to the method in which variations in the emitted gases caused by variations in culturing conditions are taken account of by providing an enlarged reference database which incorporates reference measurements taken under a variety of culturing conditions. However, both of these documents are primarily concerned with the detection of microorganisms from a single measurement made on a single culture, be it a plate culture or an in vivo measurement on a patient.
The present invention provides an alternative method for detecting microorganisms in which microorganism are cultured on a plurality of culturing media and measurements are made of each culture. In a primary, but non-limiting, embodiment, measurements are made of gaseous atmospheres associated with each culture. The method has been demonstrated to differentiate between different strains of a common microorganism species, and can provide multivariate data using fewer sensors than required in the methods of WO95/133849 and WO98/29563.
For the avoidance of doubt, the term xe2x80x9cgaseousxe2x80x9d is understood to encompass all species present in the gas phase, including volatile species.
According to the invention there is provided a method for detecting microorganisms comprising the steps of:
providing a plurality of cultures by culturing said microorganisms on a plurality of different media;
making measurements of the cultures;
collating the measurements of the cultures; and
correlating the collated measurements with the presence of the microorganisms.
Gaseous measurements of the cultures may be made by detecting gaseous species present in gaseous atmospheres associated with each of the cultures using one or more gas sensors.
The method may identify the genus of the microorganisms. Additionally, the species of the microorganisms may be detected. Additionally still, the strain of the microorganisms may be detected.
The microorganisms may comprise bacteria, viruses, microfungi, algae, yeasts, mammalian cells and/or plant cells.
The step of collating the measurements may comprise assigning a descriptor to describe a plurality of measurements.
The step of collating the measurements may comprise obtaining ratios of sensor responses. Responses obtained by measuring different cultures may be ratioed. Alternatively, or additionally, responses obtained from different sensors may be ratioed.
The gas sensor or sensors may comprise a gas sensitive material. Gaseous species may be detected by detecting an electrical, piezoelectrical or optical property of the gas sensitive material.
The gas sensitive material may comprise conducting polymer.
A mass spectrometer may be used to detect gaseous species.